ServiceWorker: add ServiceWorkerClients.claim() support (2/3).

content/browser/service_worker/service_worker_registration.h

Index: content/browser/service_worker/service_worker_registration.h
diff --git a/content/browser/service_worker/service_worker_registration.h b/content/browser/service_worker/service_worker_registration.h
index 6a8d11fcac988e4ed81c51d19563e83879575f50..994a4657a0378b5eb108cc2a8d1cbdd2699d8be0 100644
--- a/content/browser/service_worker/service_worker_registration.h
+++ b/content/browser/service_worker/service_worker_registration.h
@@ -109,6 +109,10 @@ class CONTENT_EXPORT ServiceWorkerRegistration
   // initiated immediately.
   void ActivateWaitingVersionWhenReady();
 
+  // Takes over control of provider hosts which are currently not controlled or
+  // controlled by other registrations.
+  void ClaimClients();
+
   // Triggers the [[ClearRegistration]] algorithm when the currently
   // active version has no controllees. Deletes this registration
   // from storage immediately.